The present invention relates generally to pneumatic tires, and more specifically to the tread reinforcing structures of pneumatic tires.
Pneumatic tires and other elastomeric articles are generally reinforced with cords having substantially round cross-sectional configurations. These cords either comprise a single filament or a plurality of filaments twisted together. It is also well known that these cords can be made of steel.
There has been some attempt in the prior art to specify flat wire as a reinforcement for pneumatic tires and other elastomeric products. Examples of such attempts are U.S. Pat. Nos. 4,011,899, 3,794,097 and 4,106,957.
A pneumatic tire is a complex dynamic article of manufacture and requires that the reinforcing structure go through many repeating stress strain cycles throughout its life. Therefore, it is important that the cord used in the reinforcing structure be properly designed and have the appropriate strength and fatigue properties.
There are disclosed herein structures having a combination of features which provide sufficient strength for reinforcing the tread portion of a pneumatic tire yet have sufficient ductility to provide improved fatigue characteristics.
The use of flat wires as reinforcing elements in pneumatic tires provides the tire designer with the capability of designing tires having improved running temperatures in the tread area of the tire, impact resistance, tread wear and other performance characteristics. As used herein and in the claims "flat wire" is understood to mean a single steel element having a rectangular cross section. It is understood that for the purposes of this description and the claims attached hereto the flat wire reinforcements may have either rounded corners or squared off corners and still be within the scope of this invention. (If the reinforcements are manufactured by slitting a sheet of steel, the corners may be squared; but if the reinforcements are manufactured by cold working a round wire into a rectangular reinforcement, the corners may remain rounded.) However, in order to realize these benefits it is necessary that the wire have a particular physical structure. There is disclosed herein a particular combination of structural features for a flat wire reinforcement so as to enable it to be used as a reinforcement member in pneumatic tires.